Trailer (Addon version): https://youtu.be/0_yJHuDACOQ

Native (new) version:

SSGI implemented as a modified screen space reflections shader in a custom Blender build that has a secondary layer for diffuse reflections. Both SSR layer settings are consolidated under “Screen Space Raytracing” in Eevee render settings. 

Warning – current builds are based on on experimental Blender builds and it is not recommended to save over files without backup due to potential data loss. 
Native updates:

• SSGI Native 1.0 First version of native SSGI implementation in a Blender 2.93 alpha build.
• SSGI Native 1.1 Compatible with newer master. Fixed translucent shader.
• SSGI Native 1.11 Fixed diffuse input not being masked by metallic in Principled BSDF. (Issue introduced in 1.1)
• SSGI Native 1.12 Fixed glossy input being skipped when no SSR present – globally or per node. Fixed some alpha issues. Fixed SSGI settings being reset on every file open.
• SSGI Native 1.13 Updated to be compatible with latest Blender master, redone based on the newest SSR shader with small improvements and better half resolution trace resolve. 
• SSGI Native 1.13 Updated latest version on 2.93.1 to include fixes for some GPU crashes (Fixes by Procedural). Added back link to external download of Mac, Linux and experimental builds (1.14 with wip denoising and broken half res trace).

Addon (old) version:

Addon for Blender that converts Diffuse and Principled BSDFs to nodegroups that give representation of diffuse component to SSR for SSGI effect.

Addon disclaimer: World/HDRI lighting in specular component is not handled properly between object reflections and gives inverted colors with the addon only version.

The addon (ab)uses Eevees built in screen space reflections with material nodes and thus won’t be comparable to a correctly built in SSGI solution.

The addon version currently doesn’t preserve keyframes on diffuse and principled BSDF nodes. 

Addon updates:

• 0.1.0 Fixed error in folder structure in initial release. Now installs correctly.
• 0.1.1 Added color range input clamp. Changed the way increasing intensity works. New defaults only compatible with no world/hdri lighting.
• 0.1.2 Added controls over World Material (broken glossy interaction disabled by default). Added option to scatter diffuse normals (base performance cost increased). UI and default settings changes. Clean up.
• 0.1.3 (Compatible with blender 2.91 versions from Oct.21 2020 onwards) Added refresh materials functions that preserves all possible settings while cleaning and updating materials. Added option for cubemap only bake. UI improvments.
•  0.1.4 Temporary fix for incorrect intensity in fresnel with metallics.

Info about futher plans:

Addon version will receive only minor updates since there are fundamentals issues that can’t be fixed without modifying Blender source code. Since official implementation of SSGI in Eevee 2 in Blender 3.0+ was announced, this Native version will only receive experimental updates if any.

More info on Blender Artists Thread:

Refund policy: If you chose to support it and want a refund for any reason, send the email used while making the purchase either to the email attached to the Gumroad receipt or to  a000451000@gmail.com. Sending a direct message on blenderartists.org to account “0451” with the purchase email cited is also an option. 

Alternative download links:
Native builds
Addon (old)